1. Field of the Invention
This invention relates to cleaning devices for video tape recorders, and more particularly to cleaning devices which operate on all of the operating heads and tape guides in the recorder tape path.
2. Description of the Prior Art
During normal operation of a video tape recorder, deposits from the video tape can accumulate on the internal recorder elements, causing a fuzzy or "snowy" picture and distorted sound. The picture and sound distortion becomes worse with each successive playback as the deposits continue to accumulate. In an attempt to resolve this problem, several cleaning devices are presently available on the market for cleaning the internal elements of a video tape recorder and restoring a clear picture and good sound quality.
In one popular type of cleaning device an abrasive cleaning tape is packaged in a standard video tape cassette. The cleaning cassette is inserted into the recorder and played in the standard manner so that the abrasive tape surface acts against the various internal operating heads and tape guides to remove accumulated deposits. The tape is provided with transparent leaders at each end which permit the completion of a light path between a standard light source and sensors within the recorder, thus signalling the end of the tape and the completion of a full tape pass. A typical cleaning cassette of this type is provided by the 3M Company under the trademark Scotch.
While the above type of prior art tape cleaner effectively removes accumulated deposits, their abrasive surfaces can damage the tape heads through excessive use. It is typically recommended that only two to four passes of the tape be made at any time, in order to avoid excessive wear. For example, the 3M Company cleaning cassette referred to above provides a specially recorded test message which is displayed on the screen as the cleaning tape is run. One monitors the screen to observe when the test message becomes clear, indicating that the heads have been cleaned. At that point the operator quickly stops the tape to avoid excessive wear on the heads. Even with this type of safeguard, however, it is possible to allow the cleaning tape to run for too long and damage the recorder.
Another type of tape cleaner is exemplified by the product produced by Allsop Corporation. This tape cleaner uses a non-abrasive synthetic suede material, thus avoiding the problems of excessive wear inherent in the more common abrasive tapes. The cleaning tape is relatively heavy, being about 0.025 inch (0.6 mm) thick. Rather than running the tape along the normal tape path as with the abrasive cleaners, in the Allsop device the tape is extended so that it wraps only about one-sixth of the circumference of the rotating drum that carries record/play heads, contacts only about the lower fourth of the portion of the drum so that it does not touch and clean the entire drum and grooves, and remains stationary as the drum rotates against the tape. While this device cleans the lower quarter of the drum without the wear problem introduced by the abrasive tapes, the cleaning action is not as efficient because of the relatively lesser amount of contact between the cleaning tape and the drum. Furthermore, the Allsop device does not clean any of the recorder operating heads or tape guides other than the record/play head, pinch roller and capstan drive. It also lacks a protective door to protect the tape.
The transparent leaders referred to above are added at each end of some conventional abrasive cleaning tapes for use on VHS video tape recorders; for some Beta video tape recorders a flexible metallic conductive leader is attached to each end of the tape to activate the recorder's shut off device. Both the transparent and metallic leaders are subject to breakage and make the tapes more difficult to produce. The Allsop VHS cleaning tape provides an opening toward the end of the tape itself, rather than a transparent leader. However, since the Allsop tape is not run through the recorder but is only extended far enough to make contact with the record/play head and is thereafter retracted, the completion of a light path through the opening in the tape merely indicates the maximum extension of the tape, allowing only a momentary contact between the cleaning tape and the rotating head.
In the Allsop device a portion of the cleaning tape is first moistened with a fluorocarbon cleaning fluid. The fluid is applied to the exposed portion of the tape. Leaving the tape exposed however, makes it possible for dirt to lodge on the tape and for people to foul the tape by handling it.
Another example of a cleaning device is shown in Clausen, U.S. Pat. No. 4,387,411 (1983). There is shown a cleaning tape that is withdrawn from the cassette and wrapped partially around the rotating head in a manner similar to video tape. Because the cleaning tape is thicker it exerts greater friction on the rotating recorder/playback head than video tape exerts, the cleaning tape may not feed through the recorder and can actually stop the head from rotating so that it ceases its cleaning action.
The cleaning tape in this patent is pulled into contact with the rotating head and the erase and audio heads by tape guides of the recorder that fit into indentations in the front face of the cassette housing behind the tape when the cassette housing is properly inserted into the recorder. When the recorder is actuated, these guides pull the tape out of the cassette into contact with the rotating record/playback video heads and the other head. Applicant's patent U.S. Pat. No. 4,462,056 teaches partially limiting the travel of at least one of the movable guides to prevent over-tensioning of the tape against the heads in the recorder. The device protrudes somewhat from the front face of the cassette.